The terms base station, wireless transmit/receive unit (WTRU) and mobile unit are used in their general sense. As used herein, a wireless transmit/receive unit (WTRU) includes, but is not limited to, a user equipment, mobile station fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. WTRUs include personal communication devices, such as phones, video phones, and Internet ready phones that have network connections. In addition, WTRUs include portable personal computing devices, such as PDAs and notebook computers with wireless modems that have similar network capabilities. WTRUs that are portable or can otherwise change location are referred to as mobile units. When referred to hereafter, a base station is a WTRU that includes, but is not limited to, a base station, Node B, site controller, access point, or other interfacing device in a wireless environment.
Wireless telecommunication systems are well known in the art. In order to provide global connectivity for wireless systems, standards have been developed and are being implemented. One current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2G) and was followed by its revision (2.5G). GPRS and EDGE are examples of 2.5G technologies that offer relatively high speed data service on top of (2G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute—Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3GPP) was formed in December 1998. 3GPP continues to work on a common third generational mobile radio standard.
A typical UMTS system architecture in accordance with current 3GPP specifications is depicted in FIG. 1. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an interface known as Iu which is defined in detail in the current publicly available 3GPP specification documents. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit receive units (WTRUs), shown as user equipments (UEs) as in 3GPP, via a radio interface known as Uu. The UTRAN has one or more radio network controllers (RNCs) and base stations, shown as Node Bs as in 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. One or more Node Bs is connected to each RNC via an interface known as Iub in 3GPP. The UTRAN may have several groups of Node Bs connected to different RNCs; two are shown in the example depicted in FIG. 1. Where more than one RNC is provided in a UTRAN, inter-RNC communication is performed via an Iur interface.
Communications external to the network components are performed by the Node Bs on a user level via the Uu interface and the CN on a network level via various CN connections to external systems.
In general, the primary function of base stations, such as Node Bs, is to provide a radio connection between the base stations' network and the WTRUs. Typically a base station emits common channel signals allowing non-connected WTRUs to become synchronized with the base station's timing. In 3GPP, a Node B performs the physical radio connection with the UEs. The Node B receives signals over the Iub interface from the RNC that control the radio signals transmitted by the Node B over the Uu interface.
A CN is responsible for routing information to its correct destination. For example, the CN may route voice traffic from a UE that is received by the UMTS via one of the Node Bs to a public switched telephone network (PSTN) or packet data destined for the Internet.
The RNCs generally control internal functions of the UTRAN. The RNCs also provides intermediary services for communications having a local component via a Uu interface connection with a Node B and an external service component via a connection between the CN and an external system, for example overseas calls made from a cell phone in a domestic UMTS.
Typically an RNC oversees multiple base stations, manages radio resources within the geographic area of wireless radio service coverage serviced by the Node Bs and controls the physical radio resources for the Uu interface. In 3GPP, the Iu interface of an RNC provides two connections to the CN: one to a packet switched domain and the other to a circuit switched domain. Other important functions of the RNCs include confidentiality and integrity protection.
In many wireless communication systems, adaptive transmission power control algorithms are used. In such systems, many communications may share the same radio frequency spectrum. When receiving a specific communication, all the other communications using the same spectrum cause interference to the specific communication. As a result, increasing the transmission power level of one communication degrades the signal quality of all other communications within that spectrum. However, reducing the transmission power level too far results in undesirable received signal quality, such as measured by signal to interference ratios (SIRs) at the receivers. In 3GPP W-CDMA systems, power control is used as a link adaptation method. Dynamic power control is applied for dedicated physical channels (DPCH), such that the transmit power of the DPCHs is adjusted to achieve a quality of service (QoS) with a minimum transmit power level, thus limiting the interference level within the system.
One approach is to divide transmission power control into separate processes, referred to as outer loop power control (OLPC) and inner loop power control (ILPC). Basically, the power level of a specific transmitter is based on a target SIR value. In outer loop power control, as a receiver receives the transmissions, the quality of the received signal is measured. The transmitted information is sent in units of transport blocks (TBs), and the received signal quality can be monitored on a block error rate (BLER) basis. The BLER is estimated by the receiver, typically by a cyclic redundancy check (CRC) of the data. This estimated BLER is compared to a target quality requirement, such a target BLER, representative of QoS requirements for the various types of data services on the channel. Based on the measured received signal quality, a target SIR adjustment control signal is generated
In 3GPP wideband code division multiple access (W-CDMA) systems utilizing time division duplex (TDD) mode, the UTRAN (SRNC-RRC) sets the initial target SIR to the WTRU at the call/session establishment and then subsequently continuously adjusts the target SIR of the WTRU during the life term of the call as dictated by the observation of the uplink (UL) BLER measurement.
In closed inner loop power control, the receiver compares a measurement of the received signal quality, such as SIR, to a threshold value. If the SIR exceeds the threshold, a transmit power control (TPC) command to decrease the power level is sent. If the SIR is below the threshold, a TPC command to increase the power level is sent. Typically, the TPC command is +1 or −1 bit multiplexed with data in a dedicated channel to the transmitter. In response to received TPC bits, the transmitter changes its transmission power level.
Also, a wireless channel can transmit a variety of services, such as video, voice, and data, each having different QoS requirements. The transmission rate unit is a transmission time interval (TTI). The smallest interval is one frame of data, typically defined as 10 ms for a 3GPP-like communication system. In a 3GPP-like system, TTIs are in lengths of 10, 20, 40, or 80 ms. For non-real time (NRT) data services, data is transmitted in many bursts or data sets of short duration. In a 3GPP system for example, one option is to map the data as a number of transport blocks onto a group of DPCHs which are temporarily assigned to a user by signaling an activation time and an end time with the DPCH allocation. The end time can be either explicitly signaled or can be implicitly signaled by the inclusion of a duration parameter. This temporary assignment can be called a temporary dedicated channel (Temp-DCH). This mapping is also referred to in terms of Temp-DCH allocations. One or more transport blocks are mapped onto the channel per TTI. Thus, each service is mapped across several TTIs, while target SIR adjustments are made on a TTI basis during OLPC for the Temp-DCH allocations.
During transmission of data services according to Temp-DCH allocations, a controlling RNC (CRNC) calculates initial downlink (DL) transmission power based on the target BLER, the primary common control physical channel (PCCPCH) received signal code power (RSCP), and the DL timeslot interference signal code power (ISCP) information received from the serving RNC (SRNC) and sends it to the base station. However, a mismatch typically exists between the initial transmission power and the required transmission power due to systematic and measurement bias errors. The systematic errors are related to the base station transmitter and WTRU receiver analog gain control. Measurement error occurs in the above-mentioned measured quantities. The mismatch will produce an excessive or insufficient transmission power in the beginning of each Temp-DCH allocation until the inner loop power control (ILPC) corrects these bias errors. System capacity is degraded by signal interference resulting from improper initial transmission power.